In 1975 more than four and a half billion laboratory tests costing more than 12 billion dollars were performed. The costs of interviews and other screening procedures have also soared. Accordingly, many pressures have arisen among physicians to justify the use of diagnostic procedures to the public. The purpose of this research is to clarify the value of multiple diagnostic procedures. An attempt is made to understand structural features of the evidence they provide and various influences on these features (e.g., technical method of test performance, clinical history, disease-related influences). Time series models clarify the impact of various aspects of evidence structure on the informativeness of repeated tests. The ability of a test to detect trends has much more potential influence on repeat test efficiency than the discriminatory value of single results. Rates of adaptation and latencies before the onset of changes also can have considerable significance. This is illustrated with data from repeated tests to detect colorectal cancer. Also, the value of multiple diagnosticians in suicide prediction is examined.